How the Mars Exploration Rovers Work

This illustration shows NASA's Mars Opportunity Rover, the second of the two Mars Exploration Rovers to land on the Red Planet in 2004 to search for signs of past life. NASA/JPL-Caltech

It seems easy enough: If we can blast a man to the moon for a round of golf, why do we have to send robots to Mars?

Mars, after all, is the planet that most closely resembles Earth -- that is, if Earth had an average temperature of minus 81 degrees F (minus 63 degrees C) and was ostensibly lifeless [source: Mars Exploration]. Still, its geologic patterns resemble a variety of places we're familiar with on Earth, from the ancient, flood-scarred and eroded lands of Washington state to the deserts of Death Valley and permafrost of Antarctica.

Of course, that doesn't mean that a manned mission to Mars is akin to a vacation to California. Rovers have allowed space programs to not just explore the Martian surface but also suss out some of the issues that would arise should we one day send women or men to the planet.

Dispatching a rover isn't as easy as just sending a kiddie-car with a walkie-talkie nailed to the roof. We'll be exploring both the technology and instruments used on the Mars Exploration Rovers, while also looking at how they communicate with Earth. And the technology doesn't disappoint; the rover Curiosity, launched in 2011, has instruments on it that truly belong in a science fiction movie. (Hint: lasers.)

So far, there have been more than 40 attempts to make contact with Mars. The first five missions took place from 1960 to 1962, by the former USSR. All the missions were flybys of the planet, meaning that vessels were launched into Mars' orbit to send back images. Those missions were all failures; either the spacecraft didn't make it to the planet or the spacecraft broke apart during the trip. The first successful mission was the 1964 trip by the Mariner 4, a United States craft that returned 21 images of the planet.

From then on, the United States, the former USSR, Japan and the European Space Agency have all launched missions to Mars. In the following pages, we'll explore not just the rovers themselves but also some of the discoveries they made. Let's roll to the next page to see why, exactly, we're sending rovers in the first place.

Why Send Rovers?

Those six guys are about as close as we've gotten to sending people to Mars. The six-person crew of the 520-day Mars500 mission underwent the grueling simulation of a flight to the red planet.

So if we're so advanced and fancy that we can build extremely complicated robots to Mars, why can't we just send Terry the Astronaut? The most important reason is also probably the most obvious: Terry probably just wouldn't make it there.

That is, only about a third of the missions launched thus far have been "successful," meaning that they've made a trip to Mars intact. While it's easy to be optimistic about the nearly one-third of rovers that have provided us with valuable information, it's not as easy to cheerlead a track record like that when Terry the Astronaut is in the picture. Few of us enjoy the odds of dying every three days at work.

Cost, of course, is another factor. While Curiosity, the most recent rover that's part of NASA's Mars Science Laboratory mission, cost a whopping $2.47 billion to build, NASA still didn't have to account for pesky things like allowing someone to breathe oxygen [source: Space.com]. Or return from Mars, for that matter. Keep in mind that the rovers get to stay on Mars forever when we're done with them, but Terry the Astronaut's trip is more a vacation than a move. And that means food, fuel, waste disposal and a plethora of other costs -- twice.

Beyond logistics and cost are all the vast unknowns about how the human system could react to an atmosphere like Mars. Because Mars has no magnetic field, humans would receive whopping doses of cosmic radiation -- not a problem on Earth, where the planet's magnetic field works to block it out. A 1,000-day trip to Mars has the potential to result in a 40 percent chance of the astronaut developing cancer after returning to Earth -- not necessarily something a lot of people are looking for when interviewing for a job [source: NASA Science]. Keep in mind, too, that if Terry the Astronaut is also Terry the Woman, she's at even more risk: Having breasts and female reproductive organs present nearly double the risk for cancer [source: NASA Science].

So without Terry the Astronaut signing up for massive doses of cancer-causing rays, we're left with robotic explorers. Jet over to the next page to learn about some of the missions to Mars.

Mars Exploration Background

NASA's Viking Project became the very first U.S. mission to land a spacecraft successfully on the surface of Mars. This shot shows a test version of a Viking lander in the original "Mars Yard" built at NASA's Jet Propulsion Laboratory in 1975.

The most enticing thing about Mars exploration is the promise of finding water -- or past evidence of water. "Water is key because almost everywhere we find water on Earth we find life," NASA's Web site points out. "If Mars once had liquid water, or still does today, it's compelling to ask whether any microscopic life forms could have developed on its surface."

The first missions to Mars were flybys; that means they were simply orbiting vessels that sent back photographs of the planet. The first one was Mariner 3 in 1962; however, the first successful orbit and photographs came in 1965 from Mariner 4. When the flybys ended in 1969, the next series of missions were referred to as orbiters. NASA designed these spacecraft for longer-term orbiting around Mars, collecting photographs. Mariner 9, in 1972, was the first to take photographs of the entire surface of Mars.

Orbiting missions have continued, including the 2005 launch of the Mars Reconnaissance Orbiter. The orbiter could spot objects as small as a dinner plate, while also carrying sounders to find subsurface water. Perhaps most important, it's still used as a crucial communications tool for relaying information back to mission control.

But let's wander over to the rovers' predecessors now. Viking 1 and 2, which launched in the mid-'70s, both had landers that descended to the surface of Mars. They were the first to discover that Mars was self-sterilizing, meaning that the combination of ultraviolet radiation with the dry soil and oxidizing nature of the soil chemistry prevents organisms from forming.

When we think of more modern machines landing on Mars, we usually start with the 1995 Pathfinder mission. The Pathfinder consisted of a lander, equipped with a parachute for entering Mars' atmosphere, and the Sojourner rover. The equipment returned thousands of images, as well as 15 chemical analyses of soil and weather data.

In 2003, the Mars Exploration Rover mission team launched Spirit and Opportunity, one of which was still traversing the planet as 2011 ended. Let's crawl over to the next page to learn more about those rovers, their technology and discoveries.

Spirit and Opportunity

Spirit and Opportunity, it turns out, aren't just words we use to make ourselves feel better when we're depressed. In 2003, NASA launched the cheerfully named Spirit and Opportunity rovers, which embarked on a mission of far greater mobility and distance than Pathfinder.

Both the rovers share a few noteworthy features. They can both generate power from solar panels and store it in internal batteries. Just in case any little green men are nearby, the rovers can take high-resolution color images or bust out magnifying cameras for Earthbound scientists to scrutinize objects. Multiple spectrometers on the arm of the rovers employ all sorts of tricks to determine the composition of rocks, including tracking how much heat an object is giving off and firing alpha particles at it. Spirit and Opportunity also were equipped with an installed drill (Rock Abrasion Tool) to bore into the planet's surface.

The body of the rover is called the warm electronic box (WEB). An equipment deck sits on top of the rover, where the mast (or periscope eye) and cameras reside. The gold-painted walls of the rover's body are designed to withstand minus140 degrees F (minus 96 degrees C) temperatures. Inside the WEB of the rover are lithium ion batteries, radios and electronic things like spectrometers, all requiring warmth to function. The brain of the rover is a computer that's comparable to a high-end, powerful laptop but with special memory functions that won't destruct with radiation and shut-offs. The computers also continually check temperatures to ensure a "healthy" rover.

What Spirit and Opportunity found was a credit to the technology that allowed them to explore Mars. Within a couple months of landing, the Opportunity uncovered evidence of saltwater, which leaves open the possibility that life (and fossil indications) might at one time have existed on the planet. Spirit stumbled across rocks that pointed to an earlier, unrulier Mars that was marked by impacts, explosive volcanism and subsurface water [source: NASA Mars].

We're going to learn about some features and explorations of more recent rovers, but first let's slowly traverse to the next page and look at some of the equipment and science that Spirit and Opportunity have.

Keep Rovin'

First off, it must be noted that while Spirit hasn't transmitted any messages since 2010, Opportunity was still clocking in work hours from Mars and sending information back to Earth in 2011. In fact, like any earthling, Opportunity scouts places to hole up for the winter in order to get the most solar energy stored in its batteries.

What Goes Into and Onto the Rover

This diagram shows all of the gizmos and gadgets that Spirit and Opportunity came equipped with.

Just saying that Spirit and Opportunity have cameras and some fancy radio equipment really doesn't cut it. At 384 pounds (170 kilograms) each -- and a total of $850 million to build -- you better believe the equipment is not just your trusty MacBook, superglued to an AM/FM radio.

First of all, a panoramic camera is mounted on each rover to provide a larger geologic context. Located on the mast about 5 feet (1.5 meters) off the ground, the camera doesn't just snap color images but carries 14 different filters that can identify rock and soil targets for closer looks.

A miniature thermal emission spectrometer identifies minerals at the site with a little help from infrared wavelengths. It's used to find distinctive patterns that could show water movement. On the rover arm is a Moessbauer Spectrometer, which is placed directly on samples to find iron-bearing minerals, another tool to help determine how water has affected the soil and rock.

To determine the composition of rocks, an Alpha Particle X-ray Spectrometer is used -- the same kind found in geology labs, which helps scientists determine origins and changes in the samples. The microscopic imaging tool can carefully investigate rock formation and variations.

Mars to Earth, Can You Read Me?

But how the heck do we get to actually find out about these amazing discoveries Spirit and Opportunity make? Well, it's not exactly your great-uncle's ham radio setup. While there's also a low-power and low-speed UHF radio with a meager data rate, it's primarily used as a backup, and at landing stage.

In general, the orbiters are only communicating about three hours of information directly to Earth. The rest is actually intercepted and sent to the orbiting Mars Odyssey and Mars Global Surveyor, which transmit to Earth -- and vice versa. The orbiter moves from horizon to horizon in about 16 minutes; 10 of those minutes can be used for communicating with the rovers [source: NASA]. If we were to guess, about 10 megabytes of daily data can be sent to Earth. This is especially helpful because orbiters are in closer contact with both the rovers, and have a much longer window to communicate with Earth than either rover.

The rovers each use two antennas for communication: a high-gain antenna that can steer itself to beam information toward an antenna on Earth, and a low-gain antenna that can receive and send information from every direction at a lower rate than the high-gain antenna. All these communications occur on the Deep Space Network (DSN), an international network of antennas with communication facilities in the Mojave Desert of California, Madrid, Spain, and Canberra, Australia.

Steer yourself onto the next page to learn about what a rover does on a typical day.

Curiously Strong

The Curiosity Rover that houses the Mars Science Laboratory is roughly twice the size of Spirit and Opportunity. About 10 feet (3 meters) long and 7 feet (2 meters) high, the rover weighs about 2,000 pounds (900 kilograms), and is designed with a "rocker" suspension that balances the vehicle over rocky Martian terrain.

A Day in the Life of a Rover

A map of Opportunity's travels on Sol 2756, or 2,756 days after it landed on Mars.

While the rovers aren't exactly punching a clock every morning, they do send images, along with instrument and status data, back to their Earth bosses.

Extrapolating from the data, the scientists send commands to the rover during the three-hour window of direct communication with the high-gain antenna. The rover is then on its own for 20 hours, carrying out commands and sending image data to the two overhead satellites. The rover's commanders may tell it to move toward a new rock, grind a rock, analyze a rock, take photos or gather other data with other instruments.

The rover and the scientists repeat this pattern for perhaps 90 days. At that point, the rover's power will start diminishing. Also, Mars and Earth will be getting farther and farther apart, making communication more difficult. Eventually, the rover will not have enough power to communicate, will be too far away or will run into mechanical failure, and the mission will be over

Our mission, however, is far from over. Let's take a trip to the next page where we'll learn all about the newest addition to the Mars exploration adventure.

Mars Science Laboratory and the Curiosity Rover

Illustrated here is one of the newest members of the crew roving Mars: Curiosity.

In November 2011, NASA launched the Mars Science Laboratory, which is designed to study soil and rock for organic compounds or conditions that could help us understand if Mars is -- or ever was -- able to support "habitability" of life on the planet. The Mars Science Laboratory is actually a function of the rover Curiosity, which houses the scientific instruments that will collect and analyze samples.

In 2004, NASA selected a few different proposals for investigations and equipment to include on the laboratory. Along with the United States and Canada, Spain and Russia also have instruments on the mission. Spain is studying the Rover Environmental Monitoring Station, designed to survey the atmosphere and ultraviolet rays. Russia supplied the Dynamic Albedo of Neutrons instrument, which measures hydrogen below the surface of the planet, indicating water or ice.

A suite of instruments called Sample Analysis at Mars will analyze samples. (Creative naming is not generally a priority on scientific missions.) After the rover's arm scoops up the samples, a gas chromatograph, a mass spectrometer and a laser spectrometer will measure carbon-containing compounds and isotope ratios, which indicate the history of water on Mars. An Alpha Particle X-ray Spectrometer will measure the quantity of different elements.

You'll also find the following handy instruments onboard the laboratory:

An X-ray diffraction and fluorescence indicator to detect minerals in samples

A Mars Hand Lens Imager that can take images of samples less than the width of a human hair, which is useful for detail and to get hard-to-reach photographs

A Mast Camera will take color, panoramic pictures of the surroundings, as well as record sample images. (A separate Descent Camera will capture high-definition video just before landing.)

A Radiation Assessment Detector will measure radiation so we can see if Terry the Astronaut can ever safely visit Mars -- or if any other life can exist there, for that matter.

But let's be honest: The coolest part of the Mars Science Laboratory is probably the ChemCam, which "uses laser pulses to vaporize thin layers of material from Martian rocks or soil targets up to 7 meters (23 feet) away" [source: Mars Science Lab Fact]. It will determine which atoms respond to the beam, while a telescope shows what the laser illuminates. They'll help the scientists determine what exactly they'd like the rover to travel to, or pick up. Beyond that, it's just supercool to have lasers on robots.

If you're still wandering the land hoping to learn more about our nearest planetary neighbor, navigate to the next page to learn lots more information about how intrepid Mars rovers work.